In a typical field to be irrigated, a main pipeline will be provided along one side of the field. Means must then be provided for conveying the water from the main pipeline selectively down the rows of the field. One common method for accomplishing this is to provide valves spaced along the main pipeline to which lightweight movable irrigation tubing can be selectively connected. In other words, the irrigation tubing will be connecting to one valve which will be open so that the area served by this tubing can be irrigated. After irrigating that section, the valve will be closed and the tubing will be moved to the next valve and be reconnected and that valve is reconnected. Such a system is labor intensitive. In other words, significant manpower is required to continually move the irrigation tubing and reconnect it to the respective valves.
Automatic irrigating devices have been provided which are connected to a main source of irrigation water at a central pivot and move in a circular fashion around the pivot. These devices move across the rows and therefore destroy portions of them. Furthermore, they irrigate in a circular pattern whereas most fields are laid out on a rectangular pattern which leaves portions in the corners unirrigated by this type of apparatus.
Devices have also been provided which automatically move longitudinally along the main irrigation line. Typically, such devices have been unduly complex and are subject to leakage and rapid wear of interlocking elements.
One such device is illustrated in U.S. Pat. No. 3,011,502 to Jordan having a sliding Tee connection in one embodiment and a sliding elbow connection in another embodiment. The main line has a longitudinal slit which has overlapping edges which are releasably sealed together by means of interlocking flanges. As the Tee or elbow moves longitudinally along the pipe, the interlocking edges of the main line must be continually opened and closed around the moving section. If foreign matter, such as dirt, should get in between the flange, it will interfere with the interlocking mechanism. Furthermore, the interlocking flanges are subject to wear and failure, resulting in leaks.
Another sliding valve arrangement is shown in U.S. Pat. No. 4,219,043 to Zimmerer, et al. This device also constitutes a Tee member which moves longitudinally in a main pipeline and extends through a longitudinal slit in the main pipeline which is releasably opened and closed as the device moves along. The device is subject to the same shortcomings mentioned above with respect to the Jordan patent.
Another slidable valve is shown in U.S. Pat. No. 3,019,813 to Dommann. This valve arrangement includes a separate sealing strip which releasably and sealingly engages the longitudinal slit in the main waterline. A device is provided along with a Tee connection which selectively opens and seals the longitudinal slit in the pipe as the valve moves therealong.
Still another sliding valve is shown in U.S. Pat. No. 3,592,220 to Reinke wherein the longitudinal slit in the main supply pipe has overlapping edges which can be separated by a shoe which forms a part of the Tee connection and allows the water to pass from the main supply through an outlet on the Tee.
U.S. Pat. No. 3,643,867 to Thietje discloses yet another movable valve wherein a longitudinal slit in the main irrigation pipe is closed by a longitudinal sealing member which is held in place by the water pressure within the pipe and is deflected by a device moving along the pipe to allow water from the main pipe to be transmitted to auxiliary transverse pipes extending into the field.
U.S. Pat. No. 3,903,917 to Ede discloses another irrigation system wherein the main pipeline has a longitudinal slit along the top which is closed by interlocking lips and can be selectively opened and closed in response to a movement of a slidable valve therein.